With miniaturization of small-size components, image formation devices such as a copier, a facsimile apparatus, and a printer have been developed by many manufacturers which are relatively low priced and small. Such devices can control with a high level of accuracy with the aid of a microcomputer equipped therein and are often comparable to large size apparatus in terms of the functions they perform though their storage speed is relatively slow.
A relatively large size storage apparatus processes a large number of documents in a month. Frequently these type of apparatus are used for business purposes which require a high degree of reliability. Thus, a maintenance contract is necessary to maintain the apparatus in a good working condition at all times. The maintenance expense per sheet of documents is small compared to the total number of documents processed.
On the other hand, a relatively small apparatus may process a small amount of documents per month. For small offices or households that use one such apparatus, the maintenance expense will represent a substantial portion of the cost per sheet of documents processed if they purchase a maintenance contract on a yearly basis, for example. Therefore these type of users may purchase a so-called spot maintenance contract where a serviceman is called when the apparatus malfunctions. For such a spot contract the travel expenses and technical charges are relatively expensive as compared to the cost of the parts; therefore an apparatus which allows users to replace consumable parts and parts that have a greater chance of malfunctioning would be desirable.
A duplicator, which allows the users to replace the consumable part having toner therein, has been proposed in Japanese Patent Preliminary Publications No. 57-163276. FIG. 1 illustrates the duplicator wherein a sensitive material drum 2 formed of a photo-conductive layer and an electrically conductive drum is disposed at the center of the duplicator 1. The sensitive material drum 2 is rotatable in the direction of the arrow. Around sensitive material drum 2 are positioned a corona charger (charge corotron) 3, a short focal optical element array 4, a developing machine 5, a transfer corona discharger (transfer corotron) 6, and a cleaner 7. Sensitive material drum 2, corona discharger 3, developing machine 5, and cleaner 7 form a process kit that is made as a single unit which is detachably mounted to the apparatus main body. A frame side-plate 8 supports these components in a unitary construction.
A document supporter 9 of this apparatus is illuminated by a document-illuminating lamp 10. Paper from a transfer material feeding tray 11 is delivered between delivery rollers 12 and timing rollers 13 through a guide member 14, and passes between the sensitive material drum 2 and the transfer corona discharger 6, during which a toner image is transferred. The paper to which the toner image has been transferred passes through a delivery path 15 and is fixed by a fixer (a heat roll and a pressure roll). After being fixed, the paper is discharged onto a copy tray 18 by a takeup roller 17.
This type of duplicator uses a consumable part called the process kit and the kit can be replaced by a new process kit when a malfunction occurs and damages the sensitive material drum 2. If no malfunction occurs, then the process kit can be used until all of the toner in the developing machine 5 is used up or cleaner 7 is full of toner.
The process kit or replaceable consumable part is replaced whenever it is necessary and there will be less chances of trouble if the amount of toner, etc., is set so that the kit can be replaced before its performance has deteriorated. Under such situations, the users of the duplicator are interested in the total number of copies that can still be made from that process kit or remaining copies that can be made from that kit. Thus, the process kit of this proposed duplicator is provided with a counter that counts the total time interval during which the sensitive material drum 2 is in use and total number of images formed.
FIGS. 2 to 4 illustrate a first example of the counter used in the disclosed apparatus. FIG. 2 shows a side view of a relevant portion of the process kit and FIG. 3 illustrates a front view of the process kit. A pin 20 projects from the sensitive material drum 2. Pin 20 causes a ratchet gear 21 to rotate by one tooth when the sensitive material drum 2 makes one rotation. Rotation of ratchet gear 21 is restrained by a leaf spring 22. A pin 23 projects from ratchet gear 21. One rotation of ratchet gear 21 causes ratchet gear 24 to rotate by one tooth. Rotation of ratchet gear 24 is restrained by a leaf spring 25. The ratchet gear 24, rotates in the direction of the arrow, and is secured to a disk 26 that is a life-time indicator. Disk 26 is provided with a color stripe 27, extending in radial direction. The position of the color stripe 27 is indicative of the life-time of the sensitive material drum 2.
FIG. 4 shows this proposed process kit mounted in place. A process kit cover 28 has an opening 29 through which the color stripe 27 on the disk 26 mounted on ratchet gear 24 shown in FIG. 28 can be seen when in a position indicative of the expiration of the life-time of the sensitive material drum 2.
On the other hand, FIG. 5 shows a second example of the counter used in this proposed apparatus. Sensitive material drum 2 is positioned within the kit cover 28. A count circuit 35 which is used as a measurement mechanism and a power supply 36 are disposed within the kit cover 28. Power supply 36 is arranged in such a way that when the insulative kit cover 28 is set into the the main body, a terminal 37 is inserted into a switch plug of the main body to complete a circuit including a switch 39 and a count circuit 35. The number of rotations of the sensitive material drum 2 is accumulated in accordance with the switching of ON/OFF of switch 39. Since the count circuit 35 is energized by the power supply 36 at all times, a count of the rotations over time can be stored. Thus, when the accumulated count becomes greater than a predetermined value, an LED (light emitting diode) element 40 flashes to indicate that the life time of the kit is close to expiring.
With the apparatus thus far described, the rotation of the sensitive material drum 2 is detected mechanically or electrically, and is used, accordingly, to decide the life-time of the consumable parts. This type of apparatus, however, suffers from the following problems.
(i) As shown in FIG. 1, since this proposed process kit comprises the developing machine 5, the life-time thereof expires when all of the toner is used up even if the life-time of the sensitive material drum 2 has not yet expired. The toner is a powder for developing a static latent image formed on the sensitive material drum 2 and the amount used varies greatly in accordance with the condition of the static latent image. For example, in FIG. 1, copying from a document of a relatively small size or a blackish document, with the cover of the document supporter 9 not shown being opened, causes much of toner to be used on black portions and background portions of the image to cause a considerably large amount of toner to be used. Frequent copy operation in such a manner causes the process kit to run out of toner before any indication of the expiration of the life-time of the process kit is displayed. That is, this proposed mechanical or electrical counter does not predict the life-time of a process kit in a reliable way.
(ii) On the other hand, considering the cost of a storage apparatus, the process kit should be worth the money that the user pays for the consumable parts. In the storage apparatus, the economical value of the kit should not be measured in terms of how many grams of toner can be used but should be evaluated in terms of how many copies can be made from the kit. The economical value of the consumable part can only be evaluated based on how many copies can be guaranteed. For example, if the toner leaks from developing machine 5 due to an initial problem with the consumable part, reordering a new consumable part just because the toner has run out is not economical.